Question about 340 vs. 440 (From newbie)

Hey guys,
I hardly know anything about engines and most likely won't be doing any engine builds or engine swaps for 1. not having enough room 2. and no time.

So, one day I'll be buying a Plymouth Barracuda or Roadrunner and dream about it every day.

My question is, what's the difference between the 340 and the 440? I mean, I know size-wise there's a difference, but can they be similar in speed?

From my little knowledge, I'm guessing they can be tuned to around the same power but the 440 had more potential. Why would anyone choose a car with a 340 rather than a 440? Better on gas?

How much heavier is the 440? Wouldn't that make a difference?

Sorry guys, pretty ignorant on all of this stuff. I know how knowledgable you all are so I thought you guys could help me.

Thank you!